Power shovel having isolated hydraulic dipper actuator

ABSTRACT

A hydraulic system for a power shovel may have a cylinder operatively connectable to a dipper door of the power shovel, a reservoir located at and fluidly connected to the cylinder, and an accumulator located at and fluidly connected to the cylinder in parallel with the reservoir. The hydraulic system may further have a control valve disposed between the cylinder, the reservoir, and the accumulator. The control valve may be movable to selectively direct fluid from the cylinder into the accumulator and fluid from the reservoir into the cylinder.

TECHNICAL FIELD

The present disclosure is directed to a dipper actuator and, moreparticularly, to a power shovel having an isolated hydraulic dipperactuator.

BACKGROUND

Power shovels are in a category of excavation equipment used to removelarge amounts of overburden and ore during a mining operation. One typeof power shovel is known as a rope shovel. A rope shovel includes aboom, a dipper handle pivotally connected to a mid-point of the boom,and a shovel (also known as a dipper) pivotally connected at one end ofthe dipper handle. A cable extends over a pulley at a distal end of theboom and terminates at the end of the dipper handle supporting theshovel. The cable is reeled in or spooled out by electric, hydraulic,and/or mechanical motors to selectively raise and lower the shovel.

In most rope shovels, the shovel includes a door that is selectivelyswung open to dump material from the shovel into a waiting haul vehicle.The door is pivotally connected at one edge to a shovel body, andmechanically latched at an opposing edge. A cable (historically a ropeand, hence, the term “rope shovel”) extends from an operator cabin overa boom-mounted pulley to the shovel latch. In this configuration, anoperator can actuate the latch from inside a cabin of the shovel bytensioning the cable. When the shovel is held vertically, tensioning thecable causes the latch to release the door and the door falls open underthe force of gravity. When the shovel is held horizontally, the doorswings shut against the shovel body under the force of gravity, and thelatch is biased to re-engage and hold the door in the closed position.

Although adequate for some applications, use of the cable to manuallycause actuation of the dipper latch can be problematic. In particular,typical latches and associated cable linkages are under tremendousstrain and cycle continuously. As a result, these components sufferhigh-cycle fatigue and must be serviced frequently to ensure that thelatch operates effectively when manipulated by the operator via thecable. This frequent servicing results in machine downtime and lostproductivity. Accordingly, an alternative source of power and control atthe dipper latch is desired.

One attempt to improve durability of the dipper is disclosed in U.S.Pat. No. 8,136,272 that issued to Hren et al. on Mar. 20, 2012 (“the'272 patent”). Specifically, the '272 patent discloses a dipper doorlatch having a hydraulic cylinder that is remotely activated toselectively lock and unlock movement of the door. The cylinder is adouble-acting cylinder having opposing chambers connected to each otherby way of a closed loop. A solenoid operated valve, powered by a batterypack located at the dipper, controls fluid flow between the chambers inresponse to a remotely-transmitted signal from the operator. Anaccumulator is connected to the loop to accommodate volume differencesbetween the chambers.

Although the dipper door latch of the '272 patent may have improveddurability because it no longer requires mechanical connection to thecab of the power shovel, it may still be problematic. In particular, thedouble-acting nature of the cylinder increases a complexity of the latchand the potential for malfunction. In addition, the dipper door, towhich the latch is connected, has a large amount of kinetic energy thatis not captured and reused. Further the location and configuration ofthe latch and hydraulic cylinder could result in elevated wear.

The power shovel and dipper actuator of the present disclosure solve oneor more of the problems set forth above.

SUMMARY

In one aspect, the present disclosure is directed to a hydraulic systemfor a power shovel. The hydraulic system may include a cylinderoperatively connectable to a dipper door of the power shovel, areservoir located at and fluidly connected to the cylinder, and anaccumulator located at and fluidly connected to the cylinder in parallelwith the reservoir. The hydraulic system may further include a controlvalve disposed between the cylinder, the reservoir, and the accumulator.The control valve may be movable to selectively direct fluid from thecylinder into the accumulator and fluid from the reservoir into thecylinder.

In another aspect, the present disclosure is directed to anotherhydraulic system for a power shovel. This hydraulic system may include acylinder operatively connectable between a dipper body and a base edgeof a dipper door, and an accumulator fluidly connected to the cylinder.The hydraulic system may also include a control valve disposed betweenthe cylinder and the accumulator. The control valve may be movable toselectively actuate the cylinder to release and lock pivoting movementof the dipper door.

In yet another aspect, the present disclosure is directed to a method ofoperating a power shovel. The method may include releasing fluid from acylinder to allow a dipper door of the power shovel to pivot in a firstdirection under the force of gravity, and accumulating high-pressurefluid discharged from the cylinder during pivoting of the dipper door inthe first direction. The method may also include directing low-pressurefluid from a reservoir into the cylinder during pivoting of the dipperdoor in a second direction under the force of gravity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary disclosed machine;

FIG. 1 a is a diagrammatic illustration of another exemplary disclosedmachine;

FIGS. 2-4 are schematic illustrations of an exemplary disclosedhydraulic system associated with the machines of FIGS. 1 and 1 a; and

FIG. 5 is a schematic illustration of another exemplary disclosedhydraulic system associated with the machines of FIGS. 1 and 1 a.

DETAILED DESCRIPTION

FIGS. 1 and 1 a illustrate exemplary embodiments of a machine 10.Machine 10 may perform some type of operation associated with anindustry such as mining, construction, or any other industry known inthe art. For example, machine 10 may embody an earth moving machine suchas the power shovel depicted in FIG. 1 or the dredge depicted in FIG. 1a. In the embodiment of FIG. 1, machine 10 may include a base 12, a body14 operatively connected to base 12, a gantry member 16 rigidly mountedto a top side of body 14 opposite base 12, a boom 18 pivotally connectedto a leading end of body 14, a dipper handle 20 pivotally connected to amidpoint of boom 18, a tool 22 pivotally connected to a distal end ofdipper handle 20, and cabling connecting gantry member 16, boom 18,dipper handle 20, and tool 22. In the exemplary embodiment of FIG. 1 a,machine 10 may include each of the components noted above, except thatbase 12 may be placed within a barge 12 a configured to support machine10 in aqueous and/or semi-aqueous environments.

Base 12 (or barge 12 a) may be a structural unit that supports movementsof machine 10. In the disclosed exemplary application, base 12 is itselfmovable, having one or more traction devices such as feet, tracks (shownin FIG. 1), and/or wheels that are driven to propel machine 10 over awork surface 24. In other applications, however, base 12 may be astationary platform configured for direct engagement with work surface24. As shown in FIG. 1 a, in still further embodiments, barge 12 a maybe stationary and/or moveable over a body of water, and a work surface24 a may embody an underwater trench and/or other like underwatersurface. In exemplary embodiments, at least a portion of barge 12 a maybe configured for fixed engagement with an underwater surface proximatework surface 24 a.

Body 14 may pivot relative to base 12 or barge 12 a (FIG. 1 a).Specifically, body 14 may pivot relative to base 12 or barge 12 a abouta substantially vertical axis 26. As body 14 is pivoted about axis 26,attached gantry member 16, boom 18, dipper handle 20, and tool 22 maylikewise pivot to change a radial engagement angle of tool 22 with worksurface 24, 24 a. In the exemplary embodiment of FIG. 1, tool 22typically engages with the vertical portion of work surface 24, and thehorizontal portion of work surface 24 may be formed as a result of suchengagement. The horizontal portion of work surface 24 may be removed bytool 22 in subsequent passes and/or by additional machines locatedproximate word surface 24. Alternatively, in the exemplary embodiment ofFIG. 1 a, tool 22 may engage a working face and/or other portion of worksurface 24 a disposed below the waterline (i.e., underwater). Body 14may house, among other things, a power source 28 that powers themovements of machine 10. For ease of description, the exemplaryembodiment of FIG. 1 will be referred to for the duration of thisdisclosure unless otherwise specified. It is understood, however, thatthe exemplary actuator systems and/or other components described herein,as well as their respective methods of operation, may be used with themachines 10 (i.e., the power shovel of FIG. 1 and the dredge of FIG. 1a) illustrated in either of FIGS. 1 and 1 a.

Gantry member 16 may be a structural frame member, for example a generalA-frame member, that is configured to anchor one or more cables 30 tobody 14. Gantry member 16 may extend from body 14 in a verticaldirection away from base 12. Gantry member 16 may be located rearward ofboom 18 relative to tool 22 and, in the disclosed exemplary embodiment,fixed in a single orientation and position. Cables 30 may extend from anapex of gantry member 16 to a distal end of boom 18, therebytransferring a weight of boom 18, tool 22, and a load contained withintool 22 into body 14.

Boom 18 may be pivotally connected at a base end to body 14, andconstrained at a desired vertical angle relative to work surface 24 bycables 30. Additional cables 32 may extend from body 14 over a pulleymechanism 34 located at the distal end of boom 18 and around a pulleymechanism 36 of tool 22. Cables 32 may connect tool 22 to body 14 by wayof one or more motors (not shown), such that a rotation of the motorsfunctions to reel in or spool out cables 32. The reeling in and spoolingout of cables 32 may affect the height and angle of tool 22 relative towork surface 24. For example, when cables 32 are reeled in, thedecreasing effective length of cables 32 may cause tool 22 to rise andtilt backward away from work surface 24. In contrast, when cables 32 arespooled out, the increasing effective length of cables 32 may cause tool22 to lower and tilt forward toward work surface 24.

Dipper handle 20 may be pivotally connected at one end to a generalmidpoint of boom 18, and at an opposing end to a corner of tool 22adjacent pulley mechanism 36 (e.g., rearward of pulley mechanism 36). Inthis position, dipper handle 20 may function to maintain a desireddistance of tool 22 away from boom 18 and ensure that tool 22 movesthrough a desired arc as cables 32 are reeled in and spooled out. In thedisclosed embodiment, dipper handle 20 may be connected to boom 18 at alocation closer to the base end of boom 18, although otherconfigurations are also possible. In some configurations, dipper handle20 may be provided with a crowd cylinder (not shown) that functions toextend or retract dipper handle 20. In this manner, the distance betweentool 22 and boom 18 (as well as the arcuate trajectory of tool 22) maybe adjusted.

Tool 22, in the disclosed embodiment, is known as a dipper. A dipper isa type of shovel bucket having a dipper body 38, and a dipper door 40located at a back side of dipper body 38 opposite a front sideexcavation opening 42. Dipper door 40 may be hinged along a base edge atthe back side of dipper body, so that it can be selectively pivoted toopen and close dipper body 38 during an excavating operation. Dipperdoor 40 may be pivoted between the opened and closed positions bygravity, and held closed or released by way of a dipper actuator 44. Forexample, when tool 22 is lifted upward toward the distal end of boom 18by reeling in of cables 32, a releasing action of dipper actuator 44 mayallow the weight of dipper door 40 (and any material within tool 22) toswing dipper door 40 downward away from dipper body 38. This motion mayallow material collected within tool 22 to spill out the back side. Incontrast, when tool 22 is lowered toward work surface 24, the weight ofdipper door 40 may cause dipper door 40 to swing back toward dipper body38. Dipper actuator 44 may then be caused to lock dipper door 40 in itsclosed position.

In the disclosed embodiment, dipper actuator 44 may be remotelycontrolled, such as by way of an electric signal, a hydraulic signal, apneumatic signal, a wireless signal, or another type of signal known inthe art. It is contemplated, however, that a cable may alternatively bemechanically connected to and used to activate dipper actuator 44, ifdesired.

As shown in FIG. 2, dipper actuator 44 may be a powered type of actuatorthat forms a part of an isolated hydraulic system 46 located at and, insome embodiments, mounted to tool 22. For example, dipper actuator 44may embody one or more hydraulic cylinders and/or rotary motors that areselectively actuated to initiate the door releasing/locking movementsthereof. Hydraulic system 46 may be considered an isolated system, as itmay be self-contained and self-powered, not requiring fluid connectionor powered support from other components or systems within base 12 orbody 14 of machine 10.

In the disclosed example, dipper actuator 44 is a single-acting cylinderoperatively connected between dipper body 38 and the base edge of dipperdoor 40. Specifically, dipper actuator 44 may include a tube 48, and apiston assembly 50 disposed within tube 48 to form a head-end chamber 52and a rod-end chamber 54. One of tube 48 and piston assembly 50 may bepivotally connected to dipper body 38, while the other may be pivotallyconnected to dipper door 40 by way of a link 56. As a single-actingcylinder, only one of head-end chamber 52 and rod-end chamber 54 mayever be filled with hydraulic fluid. In the exemplary configurationshown in FIG. 2, head-end chamber 52 functions as the sole pressurechamber for dipper actuator 44. As door 40 opens under the force ofgravity (see FIG. 3), piston assembly 50 may be forced to retract intotube 48, thereby discharging any fluid within head-end chamber 52 athigh-pressure from dipper actuator 44. In contrast, as door 40 closesunder the force of gravity (see FIG. 4), piston assembly 50 may beforced to extend from tube 48, thereby drawing low-pressure fluid intohead-end chamber 52. It is contemplated that rod-end chamber 54 couldalternatively function as the sole pressure chamber for dipper actuator44 (e.g., when the orientation of dipper actuator 44 is reversed), ifdesired. It is further contemplated that dipper actuator 44 couldalternatively be a double-acting cylinder. It should be noted that, insome embodiments, more than one substantially identical dipper actuator44 may be associated with a single tool 22. In these embodiments, thedipper actuators 44 may be disposed in parallel and controlledsimultaneously to cooperatively open and close dipper door 40.

Hydraulic system 46 may include additional components that interact withdipper actuator(s) 44 to selectively allow or block movement of dipperdoor 40, as well as recuperate energy associated with the movement. Inparticular, hydraulic system 46 may include a low-pressure reservoir 58,an accumulator 60, and a control valve 62 disposed between dipperactuator 44, reservoir 58, and accumulator 60. Low-pressure reservoir 58may be fluidly connected to dipper actuator 44 via a supply passage 63,while control valve 62 may be fluidly connected to dipper actuator 44via a control passage 64. Control valve 62 may also be fluidly connectedto accumulator 60 and to reservoir 58 via a high-pressure passage 66 anda low-pressure passage 68, respectively. A check valve 70 may bedisposed within supply passage 63 to help ensure a unidirectional flowof fluid from reservoir 58 into head-end chamber 52. A filter 72 may bedisposed within low-pressure passage 68 to remove debris fromcirculation within hydraulic system 46.

Reservoir 58 may constitute a low-pressure vessel configured to hold asupply of fluid. The fluid may include, for example, a dedicatedhydraulic oil for use by only dipper actuator 44. Reservoir 58 may besubstantially isolated from other circuits and systems of machine 10,and remotely located at dipper actuator 44. For the purposes of thisdisclosure, being remotely located at dipper actuator may be encompassany mounting configuration where reservoir 58 is mechanically connectedto dipper actuator 44, to dipper body 38, to dipper door 40, to link 56,and/or to the distal end of dipper handle 20 (referring to FIG. 1). Inany of these locations, the length of supply passage 63 and/orlow-pressure passage 68 may be small, thereby improving packaging and/orreliability of hydraulic system 46.

Accumulator 60 may embody a pressure vessel filled with a compressiblegas that is configured to store pressurized fluid for future use bydipper actuator 44 and/or other actuators associated with tool 22. Thecompressible gas may include, for example, nitrogen, argon, helium, oranother appropriate compressible gas. As fluid in communication withaccumulator 60 exceeds a pressure of accumulator 60, the fluid may flowinto accumulator 60. Because the gas therein is compressible, it may actlike a spring and compress as the fluid flows into accumulator 60. Whenthe pressure of the fluid within high-pressure passage 66 drops belowthe pressure of accumulator 60, the compressed gas may expand and urgethe fluid from within accumulator 60 to exit. It is contemplated thataccumulator 60 may alternatively embody a membrane/spring-biased orbladder type of accumulator, if desired. Similar to reservoir 58,accumulator 60 may be remotely located at dipper actuator 44. This maybe encompass any mounting configuration where accumulator 60 ismechanically connected to dipper actuator 44, to dipper body 38, todipper door 40, to link 56, to the distal end of dipper handle 20,and/or to reservoir 58. In any of these locations, the length ofhigh-pressure passage 66 may be small, thereby improving packagingand/or reliability of hydraulic system 46.

Control valve 62 may include a valve element 74 movable betweendifferent positions to selectively allow fluid to flow between head-endchamber 52 of dipper actuator 44, accumulator 60, and reservoir 58. Forexample, valve element 74 may be movable from a first position (shown inFIG. 2), at which fluid flow between head-end chamber 52, accumulator60, and reservoir 58, via control valve 62, may be inhibited, to asecond (shown in FIG. 3) or a third (shown in FIG. 4) flow-passingposition.

When valve element 74 is in the second flow-passing position, head-endchamber 52 may be fluidly connected to accumulator 60 such thathigh-pressure fluid discharging from head-end chamber 52 may becollected within accumulator 60. In some embodiments, when valve element74 is in the second flow-passing position, the high-pressure fluid, whenit exceeds the opening pressure of a first internal check valve, mayalso be directed into reservoir 58, if desired. In this manner,hydraulic system 46 may be protected from over-pressure events.

When valve element 74 is in the third flow-passing position, head-endchamber 52 may be fluid connected to accumulator 60 such thathigh-pressure fluid previously collected in accumulator 60 may flow backinto head-end chamber 52. In some embodiments, when valve element 74 isin the third flow-passing position and the pressure of fluid in controlpassage 64 falls below an opening pressure of a second internal checkvalve, fluid may also be drawn from reservoir 58 for supply to head-endchamber 52, if desired. In this manner, hydraulic system 46 may beprotected from voiding or cavitation caused be excessivelylow-pressures.

It is contemplated that the third flow-passing position of valve element74 may be omitted, if desired. In this alternative embodiment, head-endchamber 52 may only be replenished with fluid via supply passage 63.Alternatively, the functionality of the third flow-passing positioncould be incorporated into the second flow-passing position. That is,when valve element 74 is in the second flow-passing position, fluid mayflow through control valve 62 in either direction (i.e., from dipperactuator 44 to accumulator 60 or from accumulator 60 to dipper actuator44).

Movement of valve element 74 may be controlled to regulate operation ofdipper actuator 44 and tool 22. Specifically, valve element 74 may besolenoid operable to move from the first position to either of thesecond or third flow-passing positions based on a wired or wirelesslytransmitted control signal generated by an operator of machine 10. Valveelement 74 may be spring-biased toward the first position. When valveelement 74 is moved to the first position (referring to FIG. 2) and allfluid flow through control valve 62 is inhibited, dipper actuator 44 maybe hydraulically locked. That is, fluid within head-end chamber 52 maybe trapped when valve element 74 is in the first position, therebyblocking extension and retraction of piston assembly 50. When dipperdoor 40 is closed and dipper actuator 44 is hydraulically locked, it maynot be possible for dipper door 40 to open.

In contrast, when valve element 74 is moved to the second flow-passingposition (referring to FIG. 3), dipper actuator 44 may no longer behydraulically locked. In this state, when dipper body 38 is orientedupward (i.e., such that excavation opening 42 is oriented away from worksurface 24) and the force of dipper door 40 (and any material containedwithin dipper body 38) urges dipper door 40 to rotate clockwise (asviewed in FIG. 3) toward work surface 24, piston assembly 50 may beforced to retract within tube 48 and push fluid out of head-end chamber52 at high pressure. This high-pressure fluid, containing significantpotential energy in the form of pressure, may be directed from dipperactuator 44 through control valve 62 and into accumulator 60 where itmay be collected and stored for later use.

When valve element 74 is moved to the third flow-passing position anddipper body 38 is oriented forward (e.g., rotated about 90° clockwisefrom the upward orientation), the gravitational force acting on dipperdoor 40 may urge dipper door 40 to rotate counterclockwise (as viewed inFIG. 4), causing piston assembly 50 to extend from tube 48 and draw influid from reservoir 58 via supply passage 63 and/or accumulator 60 viacontrol valve 62.

Control valve 62 may additionally be used as a snubber for dipperactuator 44, if desired. In particular, in some embodiments, controlvalve 62 may be moveable to a position between the first and secondpositions and/or to a position between the first and third positions. Ineither of these intermediate positions, the flow of fluid from head-endchamber 52 and/or into head-end chamber 52 may be metered to a rate thateffectively slows and cushions the pivoting movement of dipper door 40.

An alternative hydraulic system 76 is illustrated in FIG. 5. Likehydraulic system 46 of FIGS. 2-4, hydraulic system 76 of FIG. 5 mayinclude dipper actuator 44, reservoir 58, accumulator 60, control valve62 supply passage 63, control passage 64, high-pressure passage 66, andlow-pressure passage 68. In addition, hydraulic system 76 may include anauxiliary actuator 78, and an auxiliary control valve 80 disposedbetween reservoir 58, accumulator 60, and auxiliary actuator 78. Alow-pressure passage 82 may connect auxiliary control valve 80 toreservoir 58; a high-pressure passage 84 may connect auxiliary controlvalve 80 to accumulator 60; and a control passage 86 may connectauxiliary control valve 80 to auxiliary actuator 78. In thisconfiguration, auxiliary control valve 80 may be configured toselectively direct high-pressure fluid that was previously collectedfrom dipper actuator 44 within accumulator 60 to auxiliary actuator 78for reuse, and return waste fluid from auxiliary actuator 78 toreservoir 58. Auxiliary actuator 78 may be, for example, an automaticgreater that provides lubricant to different pins and/or bearings oftool 22. It is contemplated that other actuators may also oralternatively be powered by the high-pressure fluid collected withinaccumulator 60, if desired.

INDUSTRIAL APPLICABILITY

The disclosed dipper actuator and associated hydraulic system may beused in any power shovel application where component longevity andreliability are desired. The disclosed dipper actuator may have improvedlongevity due to its remote power supply and wireless control. Thedisclosed dipper actuator may have improved reliability because of thereduction of conventional components (e.g., cables, wires, passages,etc.) that stretch and shrink during dipper handle extensions andretractions. Operation of hydraulic system 46 and dipper actuator 44will now be explained.

Referring to FIG. 1, the operator of machine 10 may raise, lower, andtilt tool 22 by causing cables 32 to be reeled in or spooled out. Whentool 22 is oriented in the appropriate position (oriented such that theforce of gravity generates a clockwise moment on dipper door 40) and theoperator of machine 10 desires dipper door 40 of tool 22 to open, theoperator may indicate this desire by way of an input device (not shown)located within the cabin of machine 10. A corresponding signal may begenerated and wirelessly transmitted to dipper control valve 62, causingdipper valve element 74 to move against its spring bias from its firstposition (upper position shown in FIG. 2) to its second flow-passingposition (middle position shown in FIG. 3). When valve element 74 is inits second position, dipper actuator 44 may be hydraulically unlockedand fluid within head-end chamber 52 may be free to flow through controlvalve 62 into accumulator 60 and/or into reservoir 58. At this time, thegravitational force acting on dipper door 40 may cause dipper door 40 torotate away from dipper body 38 and push piston assembly 50 into tube48. This retraction of piston assembly 50 may effectively reduce thevolume of head-end chamber 52, causing fluid to be discharged fromdipper actuator 40 at high-pressure. The high-pressure fluid may becollected within accumulator 60 for later use. In some embodiments, theflow of fluid discharging from head-end chamber 52 may be restricted tosome degree to slow and/or cushion the opening movements of dipper door40. It is important to note that movement of control valve 62 may notnecessarily result in movement of dipper door 40 or dipper actuator 44.Dipper door 40 and dipper actuator 44 may only move when tool 22 isoriented to allow gravity to pull dipper door 40 open after dipperactuator 44 has been unlocked by movement of control valve 62. If eithercondition is not satisfied (i.e., if control valve 62 has not beenunlocked or dipper door 40 is not oriented properly), dipper door 40 maynot open.

Dipper door 40 may close any time its orientation is such that gravitypulls dipper door 40 closed (i.e., any time that gravity generates amoment in the counterclockwise direction—as viewed in FIGS. 2-4). Duringthe closing movement of dipper door 40, piston assembly 50 may beretracted out of tube 48, thereby increasing the effective volume ofhead-end chamber 52. This expansion may draw fluid from reservoir 58through supply passage 63 into dipper actuator 44. It some embodiments,control valve 62 may additionally or alternatively be used to supplyfluid to head-end chamber 52, if desired. In particular, valve element74 may be moved to its third flow-passing position (lowermost positionshown in FIG. 4) during closing movements of dipper door 40. When inthis position, high-pressure fluid from within accumulator 60 may besent back to dipper actuator 44 thereby assisting the closing movementsof dipper door 40 and/or reducing a likelihood of voiding in head-endchamber 52 during the closing of dipper door 40.

Accumulator 60 may be used for different purposes and provide severalbenefits. First, collecting high-pressure fluid within accumulator 60during door opening movements may provide a back-pressure to dipperactuator 44 that resists and thereby slows the opening movements. Thiscushioning may be enhanced through metering of the fluid flowing fromdipper actuator 44 into accumulator 60. Second, the redirection ofcollected high-pressure fluid back into dipper actuator 44 during doorclosing movements may reduce a likelihood of voiding within dipperactuator 44. Third, the collected high-pressure fluid may be used as aremote power source for other actuators associated with tool 22(referring to FIG. 3). The remote and isolated nature of hydraulicsystem 46 may reduce cost and routing complexity, while at the same timeimproving durability of machine 10.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed power shoveland dipper actuator. Other embodiments will be apparent to those skilledin the art from consideration of the specification and practice of thedisclosed power shovel and dipper actuator. It is intended that thespecification and example be considered as exemplary only, with a truescope being indicated by the following claims and their equivalents.

What is claimed is:
 1. A hydraulic system for a power shovel,comprising: a cylinder operatively connectable to a dipper door of thepower shovel; a reservoir located at and fluidly connected to thecylinder; an accumulator located at and fluidly connected to thecylinder in parallel with the reservoir; and a control valve disposedbetween the cylinder, the reservoir, and the accumulator, the controlvalve being movable to selectively direct fluid from the cylinder intothe accumulator and fluid from the reservoir into the cylinder.
 2. Thehydraulic system of claim 1, wherein at least one of the reservoir andthe accumulator is mountable to a dipper body of the power shovel. 3.The hydraulic system of claim 1, wherein the reservoir and theaccumulator are fluidly connected to a single chamber of the cylinder.4. The hydraulic system of claim 1, wherein the cylinder is asingle-acting cylinder.
 5. The hydraulic system of claim 1, wherein thecontrol valve is further movable to selectively direct fluid from theaccumulator into the cylinder.
 6. The hydraulic system of claim 1,wherein: the control valve is a first control valve; and the hydraulicsystem further includes: an auxiliary actuator; and a second controlvalve configured to direct fluid from the accumulator into the auxiliaryactuator and from the auxiliary actuator into the reservoir.
 7. Thehydraulic system of claim 1, wherein motion of the dipper door is thesole source of power for pressurizing fluid in the hydraulic system. 8.The hydraulic system of claim 1, wherein the cylinder is connectablebetween a dipper body and a base edge of the dipper door.
 9. A hydraulicsystem for a power shovel, comprising: a cylinder operativelyconnectable between a dipper body and a base edge of a dipper door; anaccumulator fluidly connected to the cylinder; and a control valvedisposed between the cylinder and the accumulator, the control valvebeing movable to selectively actuate the cylinder to release and lockpivoting movement of the dipper door.
 10. The hydraulic system of claim9, wherein the accumulator is mountable to the dipper body.
 11. Thehydraulic system of claim 9, wherein the accumulator is fluidlyconnected to a single chamber of the cylinder.
 12. The hydraulic systemof claim 9, wherein the cylinder is a single-acting cylinder.
 13. Thehydraulic system of claim 9, wherein the control valve is furthermovable to selectively direct fluid from the cylinder into at least oneof the accumulator and from the accumulator into the cylinder.
 14. Thehydraulic system of claim 13, wherein: the control valve is a firstcontrol valve; and the hydraulic system further includes: an auxiliaryactuator; and a second control valve configured to direct fluid from theaccumulator into the auxiliary actuator and from the auxiliary actuatorinto a low-pressure reservoir.
 15. The hydraulic system of claim 9,wherein motion of the dipper door is the sole source of power forpressurizing fluid in the hydraulic system.
 16. A power shovel,comprising: a body; a boom pivotally connected at a base end to thebody; a dipper handle pivotally connected at a base end to a midpoint ofthe boom; a dipper pivotally connected to a distal end of the dipperhandle, the dipper having a dipper body and a dipper door pivotallyconnected at a base edge to the dipper body; a single-acting cylinderconnected at a first end to the dipper body; a link connecting anopposing second end of the single-acting cylinder to the base edge ofthe dipper door; a reservoir located at the dipper and fluidly connectedto the single-acting cylinder; an accumulator located at the dipper andfluidly connected to the single-acting cylinder in parallel with thereservoir; a first control valve disposed between the single-actingcylinder, the reservoir, and the accumulator, the first control valvebeing movable to selectively direct fluid from the single-actingcylinder into the accumulator and fluid from the reservoir into thesingle-acting cylinder; an auxiliary actuator; and a second controlvalve disposed between the accumulator and the auxiliary actuator, thesecond control valve being movable to selectively direct fluid from theaccumulator to the auxiliary actuator and from the auxiliary actuator tothe reservoir.
 17. A method of operating a power shovel, comprising:releasing fluid from a cylinder to allow a dipper door of the powershovel to pivot in a first direction under the force of gravity;accumulating high-pressure fluid discharged from the cylinder duringpivoting of the dipper door in the first direction; and directinglow-pressure fluid from a reservoir into the cylinder during pivoting ofthe dipper door in a second direction under the force of gravity. 18.The method of claim 17, further including hydraulically locking thecylinder to inhibit pivoting of the dipper door.
 19. The method of claim18, further including: directing accumulated high-pressure fluid to anauxiliary actuator; and returning low-pressure fluid to the reservoir.20. The method of claim 19, wherein motion of the dipper door is thesole source of power for pressurized fluid in cylinder.